Light-transmitting glass panels are used in various applications such as in buildings or in vehicles for allowing light to enter inside or for providing a better view. A glass panel is often used in such a manner that its principal surface extends vertically. However, when used in a ceiling window, in an automotive rear window, or in an automotive sunroof, a glass panel may be used in a tilted or horizontal state.
When a motor vehicle is fitted with a sunroof including a transparent sunroof panel such as those made of glass, for example, the sunroof brightens the interior of the vehicle and provides a sense of openness on the one hand, but may excessively brighten or warm the interior of the vehicle. To control the excessive admission of sunlight, a sunshade may be provided under the sunroof panel so as to be slidably moveable between an open position for admitting the sunlight and a closed position for blocking the sunlight.
When the sunroof is configured to enable tilting of the sunroof panel for ventilation, it may be desirable that the sunshade is integral with the sunroof panel so that the sunshade can be tilted together with the sunroof panel to allow the vehicle passenger to recognize whether the sunroof panel is opened (tilted) even when the sunshade is closed. As a sunshade device for fulfilling such a need, JP 9-249027A discloses a sunshade device including a transparent case attached to the passenger compartment side of a tiltable sunroof panel, a fixed light-polarizing film fixedly disposed in the case, a movable light-polarizing film contained in the case so as to be slidable relative to the fixed light-polarizing film, and a drive mechanism attached to the passenger compartment side of the sunroof panel to slidably move the movable light-polarizing film such that the light-blocking ratio of the sunshade device can be adjusted continuously by changing the position of the movable light-polarizing film relative to the fixed light-polarizing film.
As an alternative to a conventional mechanical sunshade, an electric sunshade has been proposed. An electric sunshade may comprise a light control film including a pair of resin films each having a transparent conductive layer coated thereon, and light control particles such as liquid crystal particles suspended in an appropriate medium disposed between the conductive layers, such that the light-transmitting and/or light-scattering characteristics of the light control film can be varied continuously by controlling the voltage applied across the conductive layers and thereby controlling the orientation of the light control particles therebetween (see JP 2009-534557A, for example). Such a light control film may be incorporated into a glass panel to provide a voltage-regulated light control sunroof panel in which the light-transmitting and/or light-scattering characteristics of the sunroof panel can be adjusted continuously by controlling the voltage applied to the incorporated light control film.
In such a sunroof panel formed by incorporating a light control film into a glass panel, it is necessary to include, in addition to the light control film, various intermediate layers such as an infrared (IR) and/or ultraviolet (UV) cut film between a pair of glass sheets, and the resulting complicated structure tends to lead to a higher cost. On the other hand, in recent years, light control films not incorporated into other devices are available at relatively low prices. Therefore, it may be considered to attach a light control film to a conventional glass panel by means of a double-sided adhesive tape or the like, and use the assembly of the light control film and the glass panel as a light control glass panel. However, when a glass panel having a light control film attached thereto is used in an application in which the glass panel may be directly exposed to sunlight, the temperature of the glass panel and the light control film may change significantly, and since the glass panel and the light control film have different thermal expansion coefficients, repeated thermal expansion and contraction may result in the light control film peeling from the glass panel, or an excessively high or low temperature may cause damage or wrinkle to the light control film.
Such problems may be created not only when a light control film is attached to a glass panel but also when any other film-shaped electric device is attached to a glass panel.